This application relates generally to a gas flow control device and, more particularly, to such a device in which full rated flow is preceded by a period of reduced flow that effects limited combustion in a burner.
The safe operation of many gas burners, particularly those enclosed in relatively compact combustion chambers, requires a start-up period of reduced gas flow preceding full rated flow. During the period of reduced flow, there is developed sufficient draft through the combustion chamber to support combustion of the subsequent full rated flow.
There have been developed and proposed various gas flow control devices, commonly known as stepped opening or slow opening valves that can delay full rated gas flow to a burner. Although many of these devices effectively accomplish the desired delay in full rated flow, they suffer from a number of individual and collective disadvantages including, for example, critical operation characteristics and high construction costs. Examples of stepped opening valves are disclosed in U.S. Pat. Nos. 3,300,174; 3,386,467; 3,351,085; 3,354,901; 3,502,101; 3,552,430; 3,578,243; 3,721,263; 3,776,268; 3,800,823; 3,880,186; 3,896,857; 4,009,861; 4,060,370; 4,217,928 and 4,254,796.
The object of this invention, therefore, is to provide an improved, relatively low cost gas flow control device that efficiently provides an initial period of reduced gas flow preceding full rated gas flow.